public class TwoIntegers {

    public int sum(int n, int m) {
        // 前置断言
        assert n >= 1 && n <= 99;
        assert m >= 1 && m <= 99;

        assert m + n <= 99;

        return n + m;
    }

    public int sub(int m, int n) {
        // 前置断言
        assert n >= 1 && n <= 99;
        assert m >= 1 && m <= 99;
        assert m - n >= 0;

        return m - n;
    }
}
